Thermal power plant utilizing compressed gas as working medium in a closed circuit including a booster compressor



F. M. WALLS 2,829,501

MEDIUM IN A CLOSED CIRCUIT INCLUDING A BOOSTER COMPRESSOR 3 Sheets-Sheet 1 mOwwwmaEOO mukmOOm x24 wwdokw mmbmmumn 30...

THERMAL POWER PLANT UTILIZING COMPRESSD GAS AS WORKING IImm Nm April 8, 1958 Filed Aug. 21, 1955 April 8, 1958 F. M. WALLS 2,829,501

THERMAL POWER PLANT UTILIZING COMPRESSED GAS AS WORKING MEDIUM IN A CLOSED CIRCUIT INCLUDING A BOOSTER COMPRESSOR Filed Aug. 21, 1953 5 Sheets-Sheet 2 '//Quw-A.

ATTORNEYS x Q Q) /N VENTO/P A Fmf/f/a/r nl. was' )30 m Jmxw v Aprxl 8, 1958 F. M. WALLS 2,829,501

rIRERMAL POWER PLANT UTILIzINC COMRRESSED CAS As' WORKING MEDIUM IN A CLOSED CIRCUIT INCLUDING A BOOSTER COMPRESSOR Filed Aug. 2l, 1955 5 Sheets-Sheet 3 F/G. 3.. F/G. 4.

j/ i aav/s/ sa 9/ wwwa@ ATTORNEYS United States Patent O THERMAL PUY/VER PLANT UTILIZING CUM PRESSED GAS AS vlilllfNG MEDIUM 1N A Clllrlllt ClRCiUli INCELUBlNG A BGDSTER CMTRESSR Frederick M., Walls, North Hollywood, Calii., assigner to l). W. Burkett, North Hollywood, Calif.

Application August 21, 1953, Serial No. 375,758

7 Claims. (Cl. oil-59) This invention has to do generally with thermal power plants which convert heat energy into torque and particularly with those in which a compressed gas `is used as the working medium to operatea lluid motor. The invention specifically relates to power plants of the type indicated in which a closed circuit system is provided for the compressed working medium so that, apart from leakage, there is no loss of the medium from the system, the gas being used repeatedly without exhausting it to the atmosphere.

This application is a continuation in part of my application for patent on Thermal Power Plant, Serial No. 30l,- 440, filed July 29, 1952, now abandoned.

lt will be apparent to those skilled in the art that this invention is not a mere modification of some orthodox heat engine but rather a novel combination of components which very effectively` converts heat ,into torque and is inherently suitable for applications where the engine operates at variable speed and load withfrequent stops and starts. While the invention has several elds of application including industrial, military and automotive, it will be evident from the objects `of the invention that the primary purpose is to provide a practical power plant for self-propelled vehicles which, because of its inherent characteristics, `eliminates the many deciencies of internal combustion and steam engines in this application.

One object is to eliminate the flywheel, clutch, transmission and power losses from long drive shafts, since the engine component can be placed directly adjacent the drive axle with the crankshaft parallel to the driving axle.

Another object is to eliminate the waste of fuel in deceleration and when the vehicle is stopped momentarily, as in trahie. p

Another object is to provide a power plant which can be adapted to burn the cheapest grades of fuel, either solid, liquid or gas.

Another object is to burn fuel at a constant rate which makes for better combustible mixturesrand eliminates obnoxious fumes.

Another object is to provide most of the advantages of the old steam-driven vehicles while avoiding the disadvantages inherent in the use of water as the working medium, such as freezing, deposits in the mechanism, and preliminary heating.

Another object of this invention is to provide a power plant for a vehicle which inherently provides a source of power for operating accessory devices.

A further object is to provide a power plant which can develop considerable power from a small engine and compressor, thereby making it practical from the standpoint of size and weight of the components, for use in self-propelled vehicles, such as automobiles, trucks, busses, military vehicles and the like where space is at a minimum.

Another object of this invention is to provide a power plant in which self-lubrication of the components is practicable. t

A further object is to provide a practical power plant in which the operating pressures and temperatures are not in excess of current practices involving commonly available materials and methods of fabrication.

Still another object is to provide a power plant in which a substantial portion of the heat used to drive the compressor may be reused, the residual heat from the compressor being carried into the high pressure side of the system.

` Another object is to provide a power plant which is easily controlled, requiring only the manipulation of a throttle valve for ordinary operation in one direction and one which does not involve the use of a gear, hydraulic,

or other type of variable transmission means. A further object of the invention is to provide a power plant which can be used as a dynamic brake to resist the driving of or overdriving of the engine component of the plant.

Still another object of the invention is to provide a powerl plant embodying a closed circulatory system for a gas under pressure which is used to drive the engine component of the system wherein means are provided in the system for utilizing the pressure differential between the gas from the exhaust side of the engine and the gas in the lov. pressure portion of the system to recompress and return a substantial proportion of the exhaust gas of the engine to the original pressure under certain operating conditions of the plant.

A still further object of the invention is to provide unique means for recompressing the gaseous working medium used in a power plant of the type indicated. In this connection it is an object to provide novel means for compressing a gas which embodies a compressor in combination with a heater so connected and operated as to utilize the energy of heated gas to recompress gas exhausted by the motor.

Afurther object is to provide a thermal power plant having a reservoir of stored power whereby there is no time lag upon starting the motor of the plant.

t These and other objects will be apparent from `the `drawings and the following description of one embodiment of the invention.

Fig. 1 is a diagrammatic or schematic representation of a thermal power plant embodying the invention and particularly showing the components of the system through which the 'working medium ilows and their relation to each other;

Fig. 2 is an electrical diagram of the electrical portion of the apparatus;

Figs. 3 to 5 are diagrammatic representations showing successive positions of two of the valves of the system; and

Fig. 6 is a diagrammatic view showing another posilion of the valves of Figs.. 3 to 5.

More particularly describing the invention, the main components thereof will first be described in their relation to each other. The system includes a high pressure storage tank 11, a low pressure storage tank 12, an engine or motor 14, connected between the two storage tanks, a booster compressor 15, a heater 16, and a heateroperated compressor 18. l also provide a feed pump 20, a throttle valve 21, and a dynamic brake valve 22.

.l prefer to use air as the Working medium. Merely by way of example and to facilitate description, it will be assumed that the system is charged so that the air is under 2000 p. s. i. in tank 11 and about 1450 p. s. i. in tank 12.

The general operation may be briefly described as follows: high pressure air is fed to the engine 14 from which it is exhausted through the throttle 21. The latter 2,829,5lll

is so constructed that when the throttle is only partially open the engine exhaust air passes to the booster compressor which serves to recompress or return about 90 percent of this emaust air to the high pressure storage tank 11. When throttle 21 is opened wider, the exhaust air bypasses the booster compressor and flows directly to low pressure storage tank 12. The compressor 18 in conjunction with the heater 16 serves to compress air taken from the low pressure storage tank and return it to the high pressure storage tank.

More particularly describing the details of the invention, the engine 14 is connected by a conduit 31 to the high pressure storage tank 11. By way of example, the engine may be a conventional reciprocating piston, steam engine type having piston valves 32 operated by a conventional linkage system, such as the Stephenson link motion. The tiow of air through the engine is controlled by throttle 21 at lthe end of the engine exhaust conduit 33. The throttle comprises a valve element 34 which is biased toward its seat by a compression spring 35 interposed between the ball and axially movable piston 36. The latter has a threaded stem 37 and an operating lever 38 for actuating it. The spring 35 is selected so that at the normal operating pressure it will hold the valve on its seat with the operating lever at oi or closed position. Upon slight retraction of piston 36, the valve opens. In this position a port leading to exhaust conduit 41 is uncovered. However, if the piston 36 is backed off far enough, a second port which communicates with an exhaust conduit 42 is uncovered.

Thus, under conditions where the throttle is opened suciently to establish communication between the conduit 33 and conduit 42, the exhaust air passes directly to the low pressure storage tank 12 or more properly to the conduit 43 which communicates therewith. This latter conduit is open to a conduit 45 having branches 46 and 47 leading to opposite ends of the central chamber 50 in the body 51 of the heater-operated compressor 18.

Since there are times when the engine will be overdriven by the mechanism to which it is connected, as for example where the engine is installed in an automobile and the latter is coasting, I provide means for passing high pressure air through the engine without permitting it to escape to the low pressure side of the system. This consists of a branch conduit 55 between conduits 31 and 33 in which is mounted a dynamic brake valve 22 and a check valve 56. The valve 22 may take the form of a valve element 57, a compression spring 58, and a piston 59. Spring 58 only lightly holds element 57 on its seat. When desired, plunger 59 may be moved inwardly to compress the spring and resist opening of the valve thereby causing the engine to act as a dynamic brake.

As previously indicated, when the load on the engine is light, and valve 21 is only partially open, the flow of engine exhaust air is to rthe booster compressor 15. This comprises a double-acting free piston-type pump, the body `of which is designated by 61. The body provides a central chamber 62 and end chambers 63 and 64. A piston 65, having a central enlargement 65', operates in the body. Conduit 41 has branches 66 and 67 leading to the opposite ends of the chamber 62. Suitable check valves 68 and 69 are provided in these branches, respectively. The ends of the chamber 62 are also connected to conduit 31, and hence the high pressure storage tank 11, by a conduit 7l) having branches '71 and 72 with check valves 73 and 74 therein, respectively.

Operatively associated with the pump is a two-position, solenoid-operated valve 75 which, in the position shown, establishes communication between conduit 41 and conduit '76 leading to the end chamber 64 of the compressor and between a conduit 77 leading from end chamber 63 of ythe compressor to a conduit 45 connecting with the low pressure storage tank. Valve 75 is operated by limit switches 80 and 81 of any conventional type actuated by the piston as it approaches the end of its stroke, the

switches being electrically connected to operate the valve 75, as will be explained later.

The booster compressor serves to compress and return about 90 percent of the exhaust gas or air from the engine to the high pressure side of the system under conditions where the load. on the engine is light and the pressure differential between the two storage tanks is sucient. To accomplish this, the ratio of the area of the large part of piston in chamber 62 to the area of an end of the piston in either end chamber is approximately 9:1. Assuming, for example, that the system is placed in operation with the high pressure storage tank containing air at 2000 p. s. i. and assuming that the exhaust gas which passes through the throttle to the booster compressor is at approximately 1950 p. s. i. (determined by construction of throttle and strength of spring therein), as is the case where the engine is operating with only light load thereon7 approximately nine volumes of air are compressed and returned to the high pressure side of the system and one volume is exhausted at approximately 1450 p. s. i. to the low pressure storage tank. Thus with valve in the position shown in Fig. l, air at approximately 1950 p. s. i. `enters chamber 62 on the right-hand side of the piston enlargement 65. Air also enters end chamber 64 at the same pressure. Chamber 63 is in communication with 'the low pressure storage tank wherein the air 'is at approximately 145() p. s. i. Thus the air ahead of the piston in chamber 62 (delivered therein on the previous stroke) is being compressed and returned to the system at 2000 p. s. i. since the total effective pressure on the piston on the right-hand side thereof is suiciently it; excess of that on the left-hand side to accomplish 't is.

As previously described, when the engine is operating under conditions of high load, making it necessary to openthe throttle wide, the exhaust air from the engine passes through conduits 33 and 42 in the low pressure side of thek system, bypassing booster compressor 15. Under such conditions, and other conditions where the pressure on the low pressure side builds up, the burner 81 in heater 16 comes on. The burner has a solenoidcontrolled valve 82, the solenoid 83 of which is controlled by a pressure-sensitive switch 84 connected into conduit 42. Closing of switch 84 serves to close the circuit through the solenoid 83 when the pressure in the line 42 rises above a predetermined figure. The burner heats air within the coil 85 of the heater and as will subsequently appear, the heated air is used to operate the heater-operated compressor 18. The heater and compressor are automatically operated through a system of solenoid controls which operates two valves, indicated by A and B. These valves are each three-position valves and are biased to a central position (the position of valve A in Fig. l) by spring means, being operated to either of the other two positions by solenoids. The coil 85, with the valves in the position shown in Figs. l and 2, is connected through valve A and a conduit 87 and thence through valve B and a conduit 88 to the outer end of a. chamber 89 in the feed pump 20. The feed pump has two such chambers, the other being indicated by 90 and connected by a conduit 91 to valve B. The inner ends of the chambers 89 and 90 of the pump are connected by conduit 92 and branches 93 and 94 to the high pressure storage tank, check valves 95 and 96 being provided in lines 93 and 94. The inner ends of the chambers 89 and 90 are also connected to the coil 85 by a conduit 97 having branches 98 and 99 with check valves 101 and 102 therein, respectively. A free, double piston 104 is employed in the pump 20. The function of the feed air is to supply a charge of air to the coil of the heater, and this is accomplished by using the force of the heated air in the coil 85 to operate the piston member with the valves A and B in the position shown in either Fig. 1 or Fig. 4.

For the purpose of controlling the valves A and B, I provide limit switches 111 and 112 operated by the compressor piston 118 and limit switches 113 and 114 operated by the piston 104 of the feed pump. The operation of these switches and the electrical circuit means and the 'Sequential positions of the valves will be described later.

As previously indicated, heated and hence compressed air in the coil 85 is used to operate the compressor 18. This consists of a body 51 with a -central chamber 50 and end chambers 116 and 117. Also, it includes a free piston 118 which is double-ended and operates in both the central and end chambers. The central chamber 50 in the piston is supplied with air from the low pressure storage tank by the conduits 45, 46 and 47. The chambers also are connected by conduit 120 and branches 121 and 122 with a conduit 124 which connects with conduit 31 `and thus establishes communication with the high pressure storage tank. The two end chambers, 116 and 117, are connected, respectively, by conduits 126 and 127 to valve A and hence in certain positions of said valve to the coil 85 of the heater.

`Thus, assuming the parts are in the position shown in Fig. l, the heated air in `coil 85 passes through valve A and valve B to the left end of the feed air pump which forces a new charge of air from the chamber of pump 20 which is in communication with conduit 98 into the coil. In this connection it should be noted that the elective piston area at the outer end of each part of the double piston 104 is greater than at the inner end thereof, making the above action possible. When piston 104 reaches the end of its travel, switch 113 is actuated and through electrical `means to be described, valves A and B are actuated to the position in which they are shown in Fig. 3, in which position coil 85 is connected to chamber 117 `of the compressor 18. The heated, high pressure air from the heater coil supplied to chamber 117 in conjunction with the air supplied to the right-hand side of piston 118 in chamber 50 serves to compress the air on the left-hand side of the piston and return it and air in chamber 116 to the high pressure side of the system. In this connection it should be noted that a conduit 129 having check valve 130, extends between valve B and line 124. When the piston reaches the end of its stroke, it operates switch 112 and this causes the valves A and B to assume the position in which they are shown in Fig. 4. rl`he heater coil then receives another charge of air and the cycle is repeated with pistons moving in the opposite directions as subsequently disclosed in connection with the sequence of switch operations.

To provide for removal of residual heat, I may employ two heat exchangers in the system apart from `the heater. The first of these is diagrammatically illustrated as a coil 41a in conduit 41 on the low pressure side of the system. The other is shown as a coil 42a in conduit 42. The coils should be in an air stream, and while this may be accomplished in several ways, fans 132 and 133 are shown to create the necessary air iiow for all conditions.

Also, to increase Vthe eiiiciency of the power plant, I prefer to insulate the high pressure storage tank and the conduits on the high pressure side of the system against loss of heat by encasing these elements in suitable heat insulation material.

In addition to the above-described parts, I provide a solenoid valve at each of the storage tanks, these being indicated by numerals 135, 136 respectively, and these valves normally would be closed until the electrical system is energized.

I also provide means for originally charging the system, comprising a filler pipe 138 provided with a valve 139 connected with the conduit 124, the latter having check valves 141 and 142 on opposite sides of pipe 138.

It is also advisable to provide pressure relief means lil titl

G in the system and this comprises a bypass line `143 having a pressure relief valve 144 of the adjustable type-and` also an air escape pipe 145 connecting with conduit 43 and having a pressure relief valve 146.

Further, suitable means may be provided for replenishing air lost through leakage, such as an auxiliary compressor 148 which can be operated by the engine or by other conventional means and connected into the high pressure side ofthe system as into conduit 31 as shown, a check valve 149 being employed between the two.

Referring now to Fig. 2, there is `shown an electrically controlled circuit means which is particularly suitable for an installation where the power plant would be installed in an automobile. It is merely exemplary and it will be obvious that many changes may be made without departing from the invention.

Referring to Fig. 2, 161 indicates a battery which is grounded as shown. Connected to the ybattery is a conductor 162` which is connected to each of the switches 111, 112, 113, and 114 and also to the solenoid 33 of the burner valve 82. This conductor is controlled by a relay 163 which is in series with the pressure switch 84 and a master switch 165 through conductors 166, 167, 168, 169. Thus when the master switch is vclosed and switch 84 is closed the relay is energized to close a circuit through the various elements which are supplied by conductor 162.

Also, l provide an override switch which is connected between conductor 166 and conductor 168 for the purpose of manually closing a circuit through the relay when desired irrespective of the position of switch 84. Associated with switch 178 is an indicator light 171 connected as shown to be energized when switch 170 is closed.

Each of the valves 135 and 136 controlling the lines from the storage tanks, respectively, is opened by energization of its respective solenoid when master switch 165 is closed, the solenoids of these latter solenoid valves being connected to conductor 168 by conductors 174 and 175, respectively.

The limit switches 80 and 8l of the booster compressor are connected in series between the battery and solenoid 181 of valve 75 by yconductor 177 and the u alternate conductors 178 .and 179 and conductor 180.

This valve is shown urged to one position by a spring 182, being actuated to the other position by solenoid 181.

As previously indicated, the valves A and B are threeposition valves which are urged to a central, normal position in which the valve A is shown in Fig. l by opposing springs 184 and 185, and 184 and 185", respectively. Valve A is actuated to its other two positions by solenoids 187 and 188 while valve B is actuated by solenoids 190 and 191.

The limit switches which are operated by the pistons of the heater compressor and feed air pump 18 and 20, respectively, are each double-pole, douhle-throw-type switches, each switch having two switch arms mechanically connected and movable to two positions. One terminal of each switch is connected to the conductor 162. One other terminal of each switch is connected to a solenoid. Thus one terminal of switch 111 is connected to solenoid 188 and one terminal of switch 112 is connected to solenoid 187. One terminal of switch 113 is connected to solenoid 190 and one terminal of switch 114 is connected to solenoid 191. The other terminals of the switches are so interconnected as shown in Fig. 2 as to cause sequential operation of the valves to the positions they are shown in Figs. l and 3-5, inclusive. When there is no current owing in conductor 162 all of the switches and their connected solenoids are without electrical energy, and the two valves A and B are in the center positions shown in Fig. 6.

When the limit switches are in the positions shown in Fig. 2, neither of the solenoids 187 or 188 of valve A is energized. However, solenoid 190 of valve B is energized through conductors 201, switch 113, conductor 202 `and switch 111 to the line 162. The sequence of the operation of the switches following the position in which they are shown in Fig. 2 is: switch 113, switch 112, switch 114, switch 111. It will lbe apparent from the electrical circuits shown in Fig. 2, without tracing each circuit that this sequential operation of switches will actuate the valves from the positions in which they are shown in Fig. 1 to that shown in Figs. 3, 4, and 5 successively and then back to the positions in which they are shown in Fig. 1.

Operation ln the operation of the apparatus, assuming there is no air under pressure in the system, the tanks are rst charged. The rst step is to close master switch 165 which energizes the electrical circuits including those to the solenoid-operated valves 135 and 136, at the high and low pressure storage tanks, opening these valves. Air is then introduced through filler pipe 138 (with valve 139 open during charging) and the system is charged until both tanks are at equal pressure which, for example, will be assumed to be about 1750 p. s. i. When the pres sure on the low pressure side reaches 1450 p. s. i., or other predetermined value, pressure-sensitive switch 84 closes, actuating relay 163 `thereby closing the circuit through solenoid 83 of the burner valve 82, opening the valve and starting the heater. With relay 163 energized, limit switches 111, 112, 113, and 114 lare all energized.

Assuming the valves A and B to be in the position in which they are shown in Fig. 1, as air in coil 85 of the heater is heated, the heated air forces the piston in the feed air pump 20 to the right which forces air on the right-hand side of the piston in chamber 89 into the coil. The travel of the piston to the right actuates switch 113 and through the electrical connections this actuates valves A and B to the positions in which they are shown in Fig. 3. Chamber 117 of the compressor 18 then receives air at an assumed approximately 3000 p. s. i. from the heater, causing the piston to move to the left until switch 112 is actuated. During the stroke of the piston the air in chamber 50 `ahead of the piston and air in chamber 116 is compressed and passes to the high side of the system. The ratio of the eifective areas of the pistons in the large and small chambers may be approximately 2:1 for the given operating temperatures and pressures.

Upon actuation of switch 112, the valves A and B are actuated to the positions in which they are shown in Fig. 4, resulting in the feed air pump 20 delivering another charge of air to the heater. At the end of its stroke from right to left, the piston in pump 20 actuates switch 114 and this results in the valves being actuated to the positions in which they are shown in Fig. 5. The compressor 18 then operates in the direction opposite to that rst described with the same result. The cycle or sequence of positions is then repeated in the order in which they are shown in Figs. 1, 3, 4, and until the pressure in the low pressure tank is at a predetermined pressure below 1450 p. s. i. at which time the pressure switch 84 breaks the circuit to the relay 163 opening the circuit to the burner valve 82 and to the limit switches.

With the system charged, high pressure air is on both side of the engine piston down to the throttle 21, assuming the Stephenson link motion has been actuated to both forward and reverse positions to accomplish this. To start the engine, the lever which controls the Stephenson link motion for forward and reverse of the engine would be placed in either of these running positions. As the throttle 21 is opened, the pressure on the spring of the throttle valve is gradually reduced to the point that the higher pressure air may escape to the low pressure iside of the system. The amount of opening of the throttle controls the pressure at which thethrottle valve opens. The throttle valve acts simi-lar to the pressure relief valve and through the adjustment of the `amount of opening of the throttle the pressure on the reverse `side of the piston is controlled so that any differential up to the pressure of the low pressure tank maybe had.

As long as the mean effective pressure is 50 p. s. i. or less (or the exhaust pressure is above 1950 p. s. i., the arbitrary figure selected as an example for the purposes of description) the air leaving the throttle goes to the booster compressor 15.

ing. In the event more power is required to overcome the load on the engine, the throttle is opened farther and the air is -bypassed directly to the low pressure tank with-` out going through the booster compressor. It may be pointed out here that with the engine in motion with the throttle lclosed as where the engine is driven by the load, the flow of air through the engine is through line 55 and the -dynamic brake. The engine in this case merely acts as a circulating pump and circulates the air at the pressure of air in the high pressure tank.

The booster compressor, for the assumed conditions, is designed with the large and small piston areas having a ratio of about 9:1. The purpose of the booster compressor is to compress about percent of the air coming 'from the throttle valve. This is accomplished as follows: with the valve in the position shown both large compartments have been lled with air at 1950 p. s. i. The small right-hand chamber 64 is also receiving air at 1950 p. s. i. Thus air in both the large right-hand compartment and small right-hand compartment is under a pressure of 1950 p. s. i. This pushes the piston to the left, compressing air in the large left-hand compartment of chamber 62 to 2000 p. s. i. The energy for this compression is obtained by exhausting chamber 63 into the low pressure tank at 1450 p. s. i., giving the necessary pressure differential on opposite sides of the piston.

Valve 75, which controls the ow of air to the booster compressor, is actuated to its two positions by limit switches 80 and 81 and the electrical circuit means previously described, to cause the compressor to continue its operation.

Whenever the pressure in the low pressure storage tank 12 exceeds 1450 p. s. i., the pressure-sensitive switch 84 closes to again operate the heater and the heater-compressor as previously described until the air in the low pressure storage tank 12 is below 1450 p. s. i.

The purpose of the override switch is to enable the operator to start the burner of the heater functioning regardless of the pressure in the low pressure storage tank. The burner will continue to function until the switch is opened. This prevents a time delay in getting the power plant and engine operating after a shutdown.

It will be apparent to those skilled in the art that many changes and modifications can be made in the power plant illustrated and described without departing from the scope of the invention as defined in the claims. The system is operable with the working fluid at various pressures and various pressure differentials, the examples given being merely by way of example. Where the system is to be operated at iluid pressures different from those given, the

ratios of the piston areas in the large and small chambers of the two compressors can be changed accordingly or this can be compensated for by adjusting the setting of the throttle and the amount of heat applied. Also, various types of fluid motors can be employed in place of the type disclosed.

The sizes in terms of displacement of the booster compressor and of the heater-operated compressor relative to the size of the engine can be Varied within wide limits, since the chief considerations are the amount of space available and the advantage of low speed operation of the compressors.

In a vehicle, this would be the same as high gear driving or practically all normal crui-s-v The power plant may be so constructed as to eliminate the necessity of the heat exchangers` 41a and 42a. For example, if the conduits on the low pressure side of the system and the low pressure storage tank are of metal having good heat conductivity and these are so placed as' to permit of air circulation thereover, the residual heat of the system will be given up by these elements. Of course, the heat losson the low pressure side of the system can be increased -by providing cooling tins on the low pressure storage tank and on any or all of the conduits on the low pressure side of the system.

Also, to increase the thermal efficiency of the plant, the coils 41a and 42a` may be so placed as to give up heat to and thus preheat air going to the heater-burner for comfbustion.

It should be apparent that `the apparatus `disclosed achieves the objects hereinbefore set forth.

While it will be apparent that standard storage tanks can be utilized operating on an assumed 2000 p. s. i. pressure in the high pressure storage tank 11, it may also be pointed out that operating temperatures need not ybe excessive to operate the compressor 18. For example, `assuming a pressure of 2000 p. s. i. on the high pressure side of the system and 1450 p. s. i. on the loW pressure side, and assuming the ratio of the small piston area to that of the large piston area in compressor 18 to be about l to 2, 3000 p, s. i. pressure of the gas heated in coil 85 would be suflicient. The temperatures required to achieve this are: assuming 2000 p. s. i. air entering the heater coil 85 to be 160 F. or about 620 Rankine, the pressure of this air would be increased to 3000 p. s. i. if heated at constant volume to about 930 Rankine. It the capacity of the coil 85 were live times that of one of the small chambers in compressor 18, it would require sucient additional heat to increase the volume of the 3000 p. s. i., 930 Rankine air one-fifth of the coil volume in order to complete one stroke of the compressor. Thus the maximum temperature of the heated air used to operate the compressor would not have to exceed ll16 Rankine, or approximately 656 F. (reference: Charles Law).

The above example is typical of a unit installed in an automobile where only a relatively small part of the gas goes through the heater, and 160 F. is a reasonable assumption of the temperature of the air entering the heater coil.

l claim:

l. In a thermal power plant utilizing gas at a pressure above atmospheric in a closed circuit, a high pressure storage tank, a low pressure storage tank, a liuid motor connected to receive gas from said high pressure storage tank, a compressor means operable by the pressure differential between gas exhausted by the motor and gas in the low pressure storage tank connected between said motor and said low pressure storage tank for receiving exhaust gas from the motor and recompressing a major portion thereof, means for conducting the recompressed gas to said high pressure tank, means for conducting the unrecompressed exhaust gas from said compressor means to said low pressure storage tank, means for permitting exhaust gas from the motor to byrpass said compressor means and flow to said low pressure storage tank when the power requirement of said motor in terms of pressure diierential exceeds a given value, means for withdrawing gas from said high pressure tank, means for confining and heating said withdrawn gas, and a second compressor means operable by the pressure differential of the pressure of gas in the highpressure storage tanls and the pressure of the heated gas for receiving gas from said low pressure storage tank, compressing the same, and delivering it to said high pressure storage tank.

2. A power plant as defined in claim 1 in which heat `exchange means is provided for extracting residual heat from the gas exhausted by the motor.

`3. A power plant as defined in claim l in which said 10 compressor means and said second compressor means are each of the doubleacting, free piston type.

4. A thermal power plant of the type utilizing gas at a pressure above atmospheric as the Working medium in a closed fluid circuit, comprising a high pressure storage tank, a low pressure storage tank, a fluid motor connected to receive gas from said high pressure storage tank, booster compressor means connected to receive exhaust gas from said motor for recompressing a portion of said exhaust gas and returning it to said high pressure storage tank, said means directly utilizing said exhaust gas as the motive power and being `operable in response to a pressure differential between said exhaust gas and the gas in said low pressure storage tank, means permitting exhaust gas to bypass said booster compressor means and How to said low pressure storage tank, a main compressor means connected to receive gas from said high pressure storage tank and deliver heated gas to said main compressor, said main compressor directly utilizing said heated gas as its motive power and being operable in response to the pressure differential between said high pressure storage tank and said heated gas, means for returning said heated gas after use thereof in said main compressor to said high pressure storage tank, aand means for extracting residual heat from the gas exhausted by said motor before said gas reaches either of said compressors.

5. In a thermal power plant having a closed fluid circuit designed to use gas at a pressure above atmospheric as the working medium, a high pressure stonage tank, a low pressure storage tank, a fluid motor connected between said tanks, a booster compressor connected to the motor on the exhaust side thereof constructed and arranged to receive exhaust gas from said motor, recompress a portion thereof and return the same to said high pressure tank and deliver the remainder to said low pressure tank, means for bypassing gas around said booster compressor to said low pressure storage tank, and heat exchange means for extracting residual heat from the gas leaving said motor before the gas reaches said booster compressor.

6. A thermal power plant having a closed uid circuit designed to use gas at a pressure above atmospheric as the working medium, a high pressure storage tank, a low pressure storage tank, a iiuid motor connected between said tanks, a booster compressor connected to the motor on the exhaust side thereof constructed and arranged to receive exhaust gas from said motor, recompress a portion thereof and return the same to said high pressure tank and deliver the remainder to said low pressure tank, means for bypassing exhaust gas from said motor around said booster compressor when the pressure dilerential required to operate the motor exceeds a given amount, a compressor connected between said low pressure storage tank and said high pressure storage tank, means for operating said last-mentioned compressor, and heat exchange means for extracting residual heat from the gas leaving said motor before said gas reaches either of said compressors.

7. In a thermal power plant utilizing gas at a pressure above atmospheric in a closed circuit, a high pressure storage tank, ya low pressure storage tank, a fluid motor connected to receive gas from said high pressure storage tank, compressor means operable by the pressure diiferential between gas exhausted by the motor and gas in the low pressure storage tank connected between said motor and said low pressure storage tank for receiving exhaust gas from the motor and recompressing a major portion thereof, means for conducting the recompressed gas to said high pressure tank, means for conducting the unrecompressed exhaust gas from said compressor means to said low pressure storage tank, means permitting exhaust gas from the motor to bypass said compressor means and ow to said low pressure storage tank when the power requirement of said motor in terms of pres- 1l sure diierentiai exceeds a given value, and means cony2,404,748 nested between said tanks for maintaining a pressure 2,592,940 differential therebetween of the gas therein.

References Cited in the le of this patent 5 175,986

UNITED STATES PATENTS zfg f 1,563,690 Cristiani Dec. 1, 1925 313:842

1,600,384 Aikman Sept. 21, 1926 12 `Salzn'iann n July 23, 1946 Monoyer Apr. 15, 1952 FOREIGN PATENTS Great Britain Mar. 15, 1923 Great Britain Aug. 30, 1928 Great Britain May 23, 1929 Germany July 25, 1919 

